One of the important things that got me through the holiday party season last year was making sure to bring a 'safe' dish and making sure to eat healthy meals the day of the party (meaning don't skip all of your meals in order to 'save up' calories, because it will probably make you go crazy and overeat junk at the party..) I tried to make sure to bring a veggie tray so I had a safe, filling option to turn to first, and then just pick out small little 'tastes' of the few dishes that looked the absolute best.
And another thing, I know it goes against the notion of not wasting food, but if you take something and it's not excellent, don't eat it! There's no sense in 'wasting calories' on something that isn't special/doesn't taste awesome.
Someone who is busier than you is working out right now.
There will come a day when you can no longer do this. Today is not that day.